Carbon/carbon parts are employed in various industries. One use for carbon/carbon parts is in the form of friction disks such as aircraft brake disks, helicopter rotor brakes, lift fan clutches, and race car brake and clutch disks. Carbon/carbon brake disks are especially useful in such applications because of the superior high temperature characteristics of C/C material. In particular, carbon/carbon material is a good conductor of heat and is able to dissipate heat generated during braking, away from the friction surfaces. Carbon/carbon material is also highly resistant to heat damage, and is thus capable of sustaining friction between brake surfaces during severe braking without a significant reduction in the friction coefficient or mechanical failure.
Carbon/carbon material is commonly formed by utilizing continuous oxidized polyacrylonitrile (PAN) fibers, referred to as “OPF” fibers. These OPF fibers are the precursors of carbon fibers and are used to fabricate a preformed shape composed of multiple layers. Typically, two or more layers are positioned onto a support plate and then needled together simultaneously or in a series of needling steps. During the needling process, multiple barbed needles are driven into the fibrous layers to displace a portion of the horizontal fibers into the z-direction. This action interconnects horizontal fiber layers into a multilayer board. Transport of the fibers by the barbed needles is a function of the stiffness and degree of freedom of the fibers, as well as other parameters. The polymeric nature of the OPF fibers allows transport of the low modulus fibers in the z-direction.
After the needling process is complete, the OPF fibers must be carbonized at high temperatures in a controlled environment to transform the preform into a high carbon content substrate. During the carbonization process, the preform loses approximately 50% of its mass and experiences a net increase in fiber density. Following this batch operation, the resulting fibrous carbon substrate is densified through chemical vapor deposition (CVD) of pyrolytic carbon until the composite reaches the target density level.
Controlling the speed of the needling process and the amount and distribution of z-fibers is an important step in the production of a preform. A higher volume of z-fibers within the preform prevents delamination in subsequent processing. A method for decreasing the amount of displaced fibers into the z-direction and obtaining higher volumes of carbon fibers within the composite without sacrificing overall composite characteristics is desired.